French presidential candidate Francois Fillon will continue campaigning in spite of a looming judicial inquiry into allegations that his family had been paid hundreds of thousands of euros for work they may not have done.

Calling the inquiry a "political assassination" the center-right candidate told a press conference it was up to the French people to decide who should be the next president.

"I will not give in, I will not surrender, I will not pull out, I'll fight to the end," he said in a speech.

Speculation over the Republican's withdrawal was sparked early Wednesday following reports that he had withdrawn from a planned visit to the Paris agricultural fair. The annual event marks a traditional pit-stop for French presidential candidates and is seen as key in winning support from France's rural communities.

It has also emerged that his children were also potentially paid funds illegitimately.

France's financial prosecutor announced Friday that it would open a judicial investigation into the allegations.

When accusations first arose against Fillon, he said that he would step down if placed under formal investigation. However, more latterly he has presented a more defiant stance, vowing to remain in the race regardless.

Reports from French news website Le Figaro said Wednesday that Fillon's campaign manager Patrick Stefanini has handed in his resignation, however it has not yet been confirmed by the party.

Speaking to CNBC earlier Wednesday, Bruno Cautrès, political science professor at Cevipof in Paris, said that France's Republican party lacks a "Plan B" and a formal investigation of Fillon would spell "disaster" for the party.

Cautrès said that Le Pen, who is currently leading the polls in the first round, could stand to benefit most from an investigation of Fillon, with the latest accusations corresponding with her claims of corruption within the traditional political system.

However, he added that Macron could stand to benefit, too, as a likely opponent to Le Pen in the second round.

France's two-round electoral process is seen as an opportunity to screen out more extreme candidates.

Analysts have so far been predicting a defeat of Le Pen in the second round. Recent polls from Odoxa suggest that Macron would defeat Le Pen by a margin of 61 percent to 39 percent in the final round.

UBS Wealth Management is also predicting odds of 40 percent that Le Pen will win the election

The first round of the French presidential election will be held on April 23. The second run-off is scheduled for May 7.